Cylindrical fuse and production thereof

ABSTRACT

An electric power fuse produced by a method comprising the steps of preparing two circular discs each having a central hole and a plurality of peripheral slits, and each slit having a lug at the radially inner end thereof, placing the circular discs at a predetermined distance, inserting fuse elements in the slits so that two ends of the fuse elements are fixed around the lugs, slipping an insulating tube over the fuse elements thus assembled, and filling the interior of the insulating tube with an arc extinguishing substance.

United States Patent [191 Wakui Aug. 20, 1974 CYLINDRICAL FUSE ANDPRODUCTION THEREOF [75] Inventor: Toshio Wakui, Kawasaki, Japan [73]Assignee: Fuji Denki Seizo Kabushiki Kaisha, Kawasaki, Japan 22 Filed:July 9, 1973 21 Appl. No.2 378,310

Related US. Application Data [62] Division of Ser. No. 223,495, Feb. 4,I972.

[58] Field of Search 337/227-237, 337/248, 251-254 3,486,155 12/1969McCaughma 337/231 FOREIGN PATENTS OR APPLICATIONS 65,130 8/1942 Norway337/231 212,513 1 1/1940 Switzerland 337/231 166,940 4/1934 Switzerland337/231 138,331 7/1934 Austria 337/231 Primary Examiner-L D. MillerAssistant Examiner-Fred E. Bell Attorney, Agent, or Firm-Holman & Stern[57] ABSTRACT An electric power fuse produced by a method comprising thesteps of preparing two circular discs each having a central hole and aplurality of peripheral slits,

and each slit having a lug at the radially inner end thereof, placingthe circular discs at a predetermined distance, inserting fuse elementsin the slits so that two [56] References Cited ends of the fuse elementsare fixed around the lugs, UNITED STATES PATENTS slipping an insulatingtube over the fuse elements thus 738,874 9/ 1903 Baby 337/231 Xassembled, and filling the interior of the insulating 2,439,674 4/1948Schuck 337/231 X tube with an arc extinguishing substance. 3,179,7744/1965 Swain 337/231 x 3,270,168 8/1966 Jacks et al. 337/231 Claim, 9Drawing Figures 20b 2b [6 I I00 20 200 I /I I I I I I I I I I I I Aup 1. 30o

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CYLINDRICAL FUSE AND PRODUCTION THEREOF BACKGROUND OF THE INVENTION Thisinvention relates generally to enclosed type power fuses and moreparticularly to an improved con- 3. Assembling of the fuse elements:

Two types are considered in the construction of spirally wound (orcoiled) fuse elements. One is constructed in the form of a corelesstype, and the other is constructed to have a core. Since the latter typeof the construction lowers the utility factor of the inside space of theprocelain tube, the former type of the construction is mostly used inhigh tension power fuses.

However, when the spiral fuse elements-of the corestruction and a methodthrough which power fuses of l typ are employed in a porcelain tube ofthe power such an organization can be assembled efficiently.

Heretofore, users of power fuses, especially of those employable inelectric power transmission and distribution: systems of voltages higherthan 3,000 V, are exertfuse, extreme care must be exercised so as toplace the fuse elements correctly without causing any entanglementbetween them. This, on the other hand, requires skilled workers, and theyield of the production of the ing much effort in acquiring power fusesof high curpower fuses l h t b n ti fa tory,

rent-limiting characteristics, accurate currentinterrupting capacities,and of uniform and reliable qualities, while the manufacturers of thepower fuses are endeavoring to produce products of guaranteed excellentcurrent-interrupting characteristics at low production cost.

In the production of electric power fuses of more than 3KV, certainpoints and factors as set forth in the following paragraphs (1) through(4) should be taken into consideration.

1. As for the fuse elements, there are two kinds, one being punched outof a flat Ag or Cu plate, and the other being of a wire form made of Agor Cu.

Although the former flat elements are economical in manufacture, thecurrent-interrupting characteristics thereof at a high potential are notsufficiently good, and elements of this type are solely employed forlowvoltage use.

Since the high tension power fuses should have sufficiently highcurrent-limiting characteristics, nevertheless maintaining a sufficientinterpolar insulating distance after the fusion of the fuse elements,wire-formed fuse elements having a relatively small cross-sectional areaare employed, and the number of the fuse elements connected in parallelis selected to suit the rated current of the power fuse. The superiorityof such a practice has been widely recognized after numerousexperiments. Furthermore, a method to fabricate each fuse element in aspiral form and enclosing such elements in a porcelain tube forelongating the interpolar distance has also been known. However,manufacture of the spiral fuse elements has been found to be ratherdifficult.

2. According to my investigation, the length and diameter of theporcelain tube used for the power fuse of different voltage and currentare as shown in the following table. Considering the fact that thegreater part of the material cost of a power fuse depends on the size ofthe porcelain tube and the fact that the space required for the powerfuse in a high tension power switchboard is of a limited nature, it isapparent that the length and diameter of the porcelain tube must beminimized as far as possible.

4. Quality control:

Because of the above described difficulty in assembling the fuseelements, X-ray tests have been conducted on some of the power fusessampled from a predetermined number of completed power fuses. However,it is apparent that such a procedure requires a considerable additionalcost, and hence raises the ultimate price of the powerfuses.

SUMMARY OF THE INVENTION Therefore, a primary object of the presentinvention method for producing electric power fuses, whereby theproduction cost of the power fuses can be substantially reduced.

Still another object of the invention is to provide a novel method forproducing electric power fuses, whereby the yield of the production canbe substantially elevated.

A further object of the invention is to provide a novel construction ofelectric power fuses whereby the current interrupting characteristics ofpower fuses can be substantially improved.

An additional object of the invention is to provide a novel constructionof electric power fuses whereby uniformity of the products can be moreeasily attained.

These and other objects of the present invention can be achieved by anovel method for producing electric power fuses comprising:

A first step comprising preparing two circular discs of differentdiameters, each circular disc having a control square hole, a pluralityof slits cut radially in a spaced apart relationship along the peripheryof the circular disc so as not to reach central square hole, and aplurality of lugs formed by folding the disc material outwardly at theinward bottom of each of the slits; and

Table 1 Voltage Rated Porcelain Tube Number of Current Length Inner dia.Elements Remarks (mm) (m 20-100 260 55 3 l0 Each element consists 3150-200 360 55 13 18 of an Ag wire of 0.1 300-400 MO 75 25 to 0.5 mmdiameter 20-30 260 55 3 5 wound into a coil of 6 40-200 360 6 l8 5 mmouter diameter. 10 30-l00 520 55 5 ll disposing the two circular discsthus prepared in a coaxially opposed but spaced apart relationship bymeans of an assembling jig so that each of the corresponding slits inthe circular discs are aligned along the length of the assembling jig;

A second step of inserting a fuse element in each pair of the alignedslits of the two circular discs with both ends of the fuse element beingfixed around the lugs provided at the bottoms of the slits;

A third step of rotating the jig intermittently around the longitudinalaxis of the jig;

A fourth step of slipping over the fuse elements thus assembled aseparately prepared insulating tube made of an inorganic, heat-resistantceramic material and having cylindrical cap-shaped terminals at bothends of the insulating tube;

A fifth step of removing the jig out of the fuse assembly after thecircular discs and the cylindrical capshaped terminals have been weldedtogether, respectively;

A sixth step of filling the interior space of the insulating tube withan arc extinguishing substancethrough one of the square holes which isleft open after the jig has been removed; and

A seventh step comprising welding end caps to both ends of thecylindrical cap-like terminals after the interior of the insulating tubehas been filled by the arc extinguishing substance.

In another aspect thereof, the invention resides in an improvedconstruction of electric power fuses comprising an insulating tube madeof an inorganic, heatresistant, ceramic material; a pair of cylindricalcapshaped terminals respectively having central holes of differentdiameters dla, dlb, and adapted to be slipped over the two ends of theinsulating ceramic tube; a pair of circular discs each being providedwith a plurality of radially extending slits distributed along theperiphery of the disc in a spaced apart relationship and with aplurality of lugs provided respectively at inner ends of the slits; saidcircular discs having diameters d2a, d2b which are selected in arelation of d2a dla d2b d1b; a jig for supporting the pair of circulardiscs apart at a predetermined distance; a plurality of fuse elementseach inserted in a pair of aligning slits in the circular discs and thetwo ends of the fuse element being fixed around said jugs; and an arcextinguishing substance introduced into the insulating tube after thefuse elements have been placed in the insulating ceramic tube.

The nature, principle, and the utility of the present invention will bemore clearly understood from the following detailed description of theinvention when read in conjunction with the accompanying drawingswherein like parts are designated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1(A) is a longitudinal sectional view of a conventional cylindricalfuse wherein the fuse elements are being assembled; I

FIG. I( B) is an end view of the fuse shown in FIG. H

FIG. 2( A) is a longitudinal sectional view of an insulating ceramictube on the two ends of which are slipped cylindrical cap-shapedterminals;

FIG. 2(B) is a right-hand end view of the insulating ceramic tube withcylindrical cap-shaped terminals;

FIG. 3(A) is a side view of fuse elements partly assembled on twocircular discs;

FIG. 3(B) is a right-hand end view of the partial assembly of FIG. 3(A)wherein elements other than the right-hand side circular disc areomitted for clarity of the view;

FIG. 3(C) is an enlarged sectional view showing a part of the circulardisc shown in FIGS. 3(A) and 3(3); and

FIGS. 4(A) and 4(8) are a longitudinal sectional view and a right-handend view, with an end cover 300a removed, of a tubular, high tension,power fuse according to the present invention.

DETAILED DESCRIPTION As conducive to a full understanding of the presentinvention, a conventional method for assembling the fuse will first bedescribed with reference to FIGS. 1(A) and 1(8). As is apparent fromthese figures, a hollow ceramic tube 1 provided with two cylindricalcapshaped terminals 20 and 2b on two ends of the tube I is mounted on afreely rotatable working frame 3. The two cap-shaped terminals 2a and 2bare provided respectively with central holes 4 of the same diameter Q3.On the outer surfaces of the cap-shaped terminals 2a, 2b, jigs "7a and7b are attached respectively for fixing temporarily two ends of fuseelements 6 (only one of the fuse elements is indicated forsimplification of the drawing).

When the fuse elements are assembled, a needle or wire 5 is passedthrough one of holes 40, also provided around the central hole 4 of thediameter d), in a direction as designated by an arrow mark A, and thetip thereof is directed through the central hole 4 of the diameter (itprovided in the cap-shaped terminal 2b. Then, one end 6a of a fuseelement 6 wound in the form of a hollow spiral is caught by the tip ofthe needle 5, and the fuse element 6 is introduced into the ceramic tube1 while the other end 6b of the element is supported by a hand of theassembling worker. When the end 6a of the element is pulled-out to theright side of the hole 4a, the end 6a is temporarily fixed on aprojection of the jig 7, and the other end 6b of the fuse element 6 ispicked, for instance, with a pincette and inserted through acorresponding hole 4b provided in the other cylindrical cap-shapedterminal 2b from the right side to the left side. The end 6b of theelement thus passed through the hole 4b is temporarily stopped on aprojection of the jig 7b on the left-side, cap-shaped terminal 2b.

A desired number of the fuse elements are assembled inside of theceramic tube by repeating the above described procedure. It will beapparent that the assembling work of the fuse elements becomesincreasingly more difficult in accordance with an increase in the fuseelements. In fact, it has required highly skilled labor to avoidentanglement of these fuse elements when their number increases, andeven with skilled labor, the occurrence of defective products has beenhigher than 15 percent.

The method for producing the high tension power fuses and a constructionof the power fuses according to this invention will now be describedwith reference to FIGS. 2 through 4.

In FIGS. 2(A) and 2(B), there is shown an insulating tube 1 made of aninorganic, heat-resistant ceramic, on the two ends of which are fixed,by means of an adhesive, two cylindrical cap-shaped terminals 2a, 2bmade of an electrically conductive material such as copper or copperalloy. The cap-shaped terminals 20 and 2b are provided with centralholes Ha and Hb of diameters dla anddlb, respectively. The insulatingceramic tube 1 with the cap-shaped terminals 2a and 2b of the abovedescribed construction is employed after fuse elements are assembled aswill be described hereinbelow for covering the fuse-element assembly.

The assembling procedure of the fuse elements will now be described withreference to FIGS. 3(a), 3(b), and 3(0).

In these figures, there are shown two circular discs 11a and 11b made ofan electrically conductive material such as copper or copper alloy andhaving diameters d2a and d2b, respectively. The circular discs 11a and11b respectively have central square holes Sa and Sb of different sizes,and each of the circular discs 11a and 11b is provided with a pluralityof radial slits 9 cut from the peripheral edge of the circular disc butnot reaching the central square hole as shown in FIG. 3(3). The materialof the circular disc is bent back outwardly at the radially inner end ofeach of the slits so that a lug 10 is thereby formed on each of theslits 9. In FIG. 3(C), one of such lugs 10 on the circular disc 11b isindicated as an example. The relation between the diameters d2a, d2b ofthe circular discs and the diameters dla, dlb of the holes in thecylindrical cap-shaped ter minals 2a and 2b is so selected that d2a dlad2b dlb.

The procedure of assembling the fuse elements is as follows. Thecircular disc terminals 11a, 11b are slipped over a specific jig in theform of a shaft 12 (indicated in FIG. 3 by oblique shading lines) whichhas portions adapted to be forced into the square holes Sa and Sb ofthe'circular disc terminals 11a, 11b.

More specifically, a circular disc 11a having a larger diameter d2a isfirst slipped over the shaft 12, from the leftward end thereof, untilthe circular disc 11a abuts against a right-hand side step delimiting afirst portion of the shaft 12 adapted to be engaged with the square hole80 of the disc 11a, and then another circular disc 11b having a smallerdiameter d2b is slipped onto the shaft 12 from the same end until thecircular disc llb abuts the second step delimiting a portion of theshaft 12 adapted to be engaged with the square hole Sb of the disc llb.With such an arrangement, the distance between the two circular discscan be automatically made equal to the distance between the twocylindrical cupshaped terminals.

Furthermore, the two square holes Sa and Sb of the circular discs 110and 11b are similar figures, and the positions of the slits 9 relativeto the corners of the square hole Sa or Sb are also definitelydetermined. As a result, when the two circular discs 11a and 11b aremounted as described above on the shaft 12, the slits 9 and 9 on thesecircular discs are disposed in alignment along the longitudinaldirection of the shaft 12.

While an example of a circular disc having eight slits equally spacedapart from each other and forming an equal angle 0 around the centerthereof is illustrated in FIG. 3(B), the number of the slits isdetermined solely by the number of the fuse elements 6 to be connectedin parallel within the tube 1. Furthermore, while the portions of theshaft 12 engaging with the square holes Su and Sb of the circular discs11a and 11b are made with square cross sections conforming to the squareholes Sa and Sb, the portions of the shaft 12 at the two ends thereofsupported by the rotatable working frame 3 are made with circular crosssections, whereby the shaft 12 can be easily rotated aboutitslongitudinal axis.

In FIG. 3(A), three fuse elements 6-1, 6-2, and 6-3 are shown to havebeen attached to the circular discs 1 la and 11b. After completion ofthe attachment of the fuse element 6-3, the shaft 12 is rotated by adriving device (not shown) intermittently in the arrow direction untilthe succeeding pair of slits 9 are brought into the uppermost position.That is, the shaft 12 is rotated intermittently through increments ofangle 0 around its longitudinal axis.

Then the fourth fuse element 64 is inserted into the slits now broughtinto the uppermost position, and the two ends thereof 6a and 6b aresecured around the lugs 10 corresponding to said fuse element 64.

Since each of the elements 6 contains a hollow helical portion, it hasresilience along its length, and also since the lugs 10 are made to havea height of about 3 mm., the elements 6 can be attached to the lugseasily without requiring the application of any excessive force whichmight reduce or deform the cross-sectional area of the fuse element.

Furthermore, as shown in the drawing, two ends 60 and 6b'of each fuseelement 6 are formed beforehand into loops. This can be accomplished bycolding the end portion of the wire-formed fuse element back for asuitable length with a portion of the wire to be formed into the loopbeing rounded through a rounding device (not shown), and the folded backportion of the wire being wound around the mating portion of the fuseelement. In the course of the assembling of the fuse elements, thelooped portions of the fuse elements are merely passed around the lugs,and after completion of the assembling, all of the portions of the fuseelements passed around the lugs may be solderedin one step.

By the above described procedure, a required number of fuseelements canbe assembled outside of the insulating tube 1, whereby the work timerequired for the assembling of the fuse elements and the occurrence ofunsatisfactory products can both be minimized, and the reliance uponskilled workers can be much reduced.

Additionally, because of the employment of the looped ends of the fuseelements, the possibility of the fuse elements being pulled within theinsulating tube during the soldering process or actual use and defectiveoperation of the power fuses can be substantially eliminated.

After the completion of the work of assembling the fuse elements, aninsulating tube 1 as shown in FIG. 2 is slipped over the fuse elements.In this case, the cylindrical cap-shaped terminal 2a having a hole l-laof a larger diameter is first slipped over the circular disc 1 lb of asmaller diameter of the fuse-element assembly, and then the insulatingtube 1 is advanced toward the circular disc 11a of a greater diameter.Because of the hereinbefore described relationship between thediameters, 1.e.,

d2a dla d2b dlb,

ultimately, the forward end a of the cap-shaped terminal 2a abutsagainst the rearward surface of the circular disc lla having a largerdiameter d2a, and the inner surface of the end portion 20b of thecap-shaped terminal 2b abuts against the rearward surface of thecircular disc 11b having a smaller diameter d2b as clearly shown in FIG.4(a). At this instant, the periphery of the circular disc 11a and theend portion 20a of the cap-shaped terminal 20 are brazed together asindicated at 30a, and the inner periphery of the hole Hb through the endportion 20b and the rearward surface of the circular disc llb are brazedtogether as indicated at 30b. The shaft 12 is pulled out of the assemblyafter completion of the above described brazing steps.

An end cover, for example, 30% is then secured by brazing over the endportion 20b, so that the square hole Sb formed through the circular disc11b is thereby closed. An arc extingushing substance such as silica isthen poured through the square hole Sa while vibration is applied to theinsulating tube 1. When the interior of the insulating tube 1 issufficiently filled with the arc extinguishing substance, the other endcover, for example, 300a is secured by brazing over the end portion 20aso that the square hole Sa is thereby closed.

Although the present invention has been described with respect topreferred embodiment thereof, it will be apparent to those skilled inthe art that various modifications and alterations may be carried outthereon without departing from the spirit and scope of the invention.For instance, the shape and construction of the cylindrical cap-shapedterminals, square holes of the circular discs, slits and pawls of thesame, etc., may be modified in various ways, and the fuse elementsthemselves may be changed to the straight wire type instead of the abovedescribed hollow helical construction. Furthermore, the rotatableworking frame 3 in FIG. 3(A) may be omitted if the shaft 12 isvertically supported with the circular disc 11a of a larger diameterplaced downward and the circular disc 11b of a smaller diameter placedupward.

According to the present invention, since the depth of the slits in thecircular discs may be suitably varied from each other, and the distancebetween each of the fuse elements may also be varied over a wide range,with a minimum value of about 5 mm, the number of the fuse elementscontained in the insulating tube 1 can be varied in a wide range,whereby the rated value of the fuse unit may be changed as desired withthe size of the insulating tube held at a minimum number of variations.

I claim:

1. An electric power fuse comprising an insulated tube made of aninorganic, heat-resistant, ceramic material; a pair of cylindricalcap-shaped terminals respectively having central holes of differentdiameters dla and dlb and adapted to be slipped over the ends of theinsulating tube; a pair of circular discs each provided with a pluralityof radially extending slits distributed along the periphery thereof in aspaced apart relationship and with a plurality of lugs providedrespectively at inner ends of the slits, said discs having diameters d2aand d2b, respectively, which are selected to conform to the relation ofd2a dla d2b dlb; said pair of circular discs being supported at apredetermined distance in an opposed relation on acommon axis; aplurality of fuse elements each inserted in a pair of slits in thecircular discs aligned with each other in the axial direction of thediscs, the two ends of each fuse element being fixed around said lugsthe fuse elements thus assembled being enclosed within the insulatedtube; and an arc extinguishing substance introduced into the insulatingtube after the fuse elements have been enclosed in the insulating tube.=l

1. An electric power fuse comprising an insulated tube made of aninorganic, heat-resistant, ceramic material; a pair of cylindricalcap-shaped terminals respectively having central holes of differentdiameters d1a and d1b and adapted to be slipped over the ends of theinsulating tube; a pair of circular discs each provided with a pluralityof radially extending slits distributed along the periphery thereof in aspaced apart relationship and with a plurality of lugs providedrespectively at inner ends of the slits, said discs having diameters d2aand d2b, respectively, which are selected to conform to the relation ofd2a > d1a > d2b > d1b; said pair of circular discs being supported at apredetermined distance in an opposed relation on a common axis; aplurality of fuse elements each inserted in a pair of slits in thecircular discs aligned with each other in the axial direction of thediscs, the two ends of each fuse element being fixed around said lugsthe fuse elements thus assembled being enclosed within the insulatedtube; and an arc extinguishing substance introduced into the insulatingtube after the fuse elements have been enclosed in the insulating tube.